Regular ArticleMetabolism and Excretion of Methylamines in Rats
Abstract
Experiments were performed with rats to examine the sources and disposition of dimethylamine (DMA), trimethylamine (TMA), and trimethylamine N-oxide (TMAO), all potential substrates for in vivo nitrosation to form N-nitrosodimethylamine (NDMA), a potent carcinogen. When bolus doses of [14C]DMA or [14C]TMA were given ip, recovery of radioactivity in the urine was essentially complete, and respiratory excretion, fecal excretion, and accumulation in tissues of these amines or their metabolites were negligible. Urine analysis following doses of stable isotopes showed that DMA was not converted to TMA or TMAO. Varying amounts of TMA were oxidized to TMAO, the fraction oxidized decreasing at higher doses of TMA. Ingestion and excretion of naturally occurring methylamines were monitored over a 5-day period in separate groups of normal and germ-free rats. The results of these metabolic balance studies indicate that there is net synthesis of DMA by gut bacteria and net consumption of TMAO by endogenous processes. The net intake or excretion of TMA and TMAO observed in normal and germ-free rats is consistent with bacterial synthesis of TMA followed by its almost complete oxidation to TMAO. Blood concentrations of DMA and TMA were measured in rats for 8 hr following <5, 100, or 1000 μmol bolus iv or ip doses of radioisotopes or stable isotopes. At any given dose of DMA or TMA, the decay in blood concentration was approximately monoexponential. At the lowest (most physiologic) dose the apparent volume of distribution (VD) for DMA was larger than that for TMA. Both values of VD greatly exceeded the size of the animals, suggesting that DMA and TMA are highly concentrated at one or more locations in the body. This was confirmed by measurements in tissue homogenates sampled 1 hr after a dose. The overall handling of methylamines by rats is generally consistent with observations in humans. The presence of high local concentrations of DMA and TMA at various extragastric sites merits further investigation in connection with the potential for endogenous nitrosation of these methylamines to form NDMA.
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Loop Diuretics Inhibit Renal Excretion of Trimethylamine N-Oxide
2021, JACC: Basic to Translational ScienceThis study demonstrates, for the first time, that renal tubular excretion of trimethylamine N-oxide (TMAO) is inhibited by concomitant loop diuretic administration. The observed marked accumulation in the renal parenchyma, and to lesser extent, plasma, implies differential distributions of TMAO across various tissues and/or systems as a consequence of efflux channel control. A better understanding of TMAO renal clearance and its potential interactions with current and future therapies in patients with heart failure are warranted.
The interaction between the gut Microbiota and herbal medicines
2019, Biomedicine and PharmacotherapyAs technologies used to study the gut microbiota have improved, the relationship between the gut microbiota and health has become increasingly obvious. Herbal medicines have been used for thousands of years, and are known to be “simple, convenient, cheap, and effective”. However, due to many factors, such as their complex composition, unclear active compounds, and poor knowledge of their underlying mechanisms, the clinical applications of herbal medicines are not widely recognized. Recently, there have been an increasing number of studies which have investigated the interaction between the gut microbiota and herbal medicines. We have found that interactions between the gut microbiota and herbal medicines occur primarily through two pathways. One pathway is that the gut microbiota “digests” the herbal medicines into absorbable active small molecules, which enter the body and induce physiological changes. The other is that herbal medicines regulate the composition of the gut microbiota and its secretions, thereby changed gut microbiota and its secretions inducing physiological changes. In summary, the interactions between the gut microbiota and herbal medicines can be attributed to absorbable active small molecules and changed gut microbiota and its secretions. Our findings will aid the exploration of the mechanisms and pathways underlying the function of herbal medicines in the future. This review also summarizes the direction of future research and the main problems faced by the current researchers.
Liver-specific metabolomics characterizes the hepatotoxicity of Dioscorea bulbifera rhizome in rats by integration of GC-MS and <sup>1</sup>H-NMR
2018, Journal of EthnopharmacologyDioscorea bulbifera rhizome (DBR), one type of herbal medicine, is extensively used in both Indian and Chinese system of traditional medicine. It has been effective in treating various diseases, such as sore throat, struma, and tumors. However, more and more clinical investigations have suggested that DBR can cause liver injury.
In the present study, we aimed to characterize the corresponding molecular changes of liver dysfunction and reveal overall metabolic and physiological mechanisms of the subchronic toxic effect of DBR.
A liver-specific metabolomics approach integrating GC-MS and 1H-NMR was developed to assess the hepatotoxicity in rats after DBR exposure for 12 weeks. Multivariate statistical analysis and pattern recognition were employed to examine different metabolic profiles of liver in DBR-challenged rats.
A total of 61 metabolites were screened as significantly altered metabolites, which were distributed in 43 metabolic pathways. The correlation network analysis indicated that the hub metabolites of hepatotoxicity could be mainly linked to amino acid, lipid, purine, pyrimidine, bile acid, gut microflora, and energy metabolisms. Notably, purine, pyrimidine, and gut microflora metabolisms might be novel pathways participating in metabolic abnormalities in rats with DBR-triggered hepatic damage.
Our results primarily showed that the liver-specific metabolic information provided by the different analytical platforms was essential for identifying more biomarkers and metabolic pathways, and our findings provided novel insights into understand the mechanistic complexity of herb-induced liver injury.
Toxicological effects of Nux Vomica in rats urine and serum by means of clinical chemistry, histopathology and <sup>1</sup>H NMR-based metabonomics approach
2018, Journal of EthnopharmacologyCitation Excerpt :The decrease in hippurate indicated that Nux Vomica affected the gut microflora (Phipps et al., 1998). Furthermore, TMAO is a product of choline degradation which involves the conversion of choline into TMA, a precursor of TMAO, by the gut microflora (Smith et al., 1994; Li et al., 2014). Thus, increased levels of TMAO in rat serum and urine suggested that Nux Vomica may induce disorder of the gut microbiota.
The dried ripe seeds of Nux Vomica (Strychnos nux-vomica L.), a traditional Chinese medicine, have been used to treat multifarious symptoms. However, the clinical applications of Nux Vomica are limited by its severe toxicity. In this study, Nux Vomica was subjected to nuclear magnetic resonance (NMR) metabonomics and pathological examination to determine relevant biomarkers in target organs and to explain the underlying toxicity mechanism.
Thirty-six male Sprague-Dawley rats were randomly divided into three groups of twelve rats. The control group was oral gavaged with distilled water, and two experiment groups were treated with Nux Vomica at a dose of 0.315 and 0.630 g/kg body weight. On days 14 and 21, serum, urine, liver and kidney tissues were collected for histopathological examination, biochemical analysis and 1H-NMR analysis.
The metabolites changes of rats treated with Nux Vomica are obviously differ from that of controls. In serum, low-dose group compared with control shows the significantly changes included elevated concentration of glucose, TMAO, and creatine, with decreased lipids, 3-HB, lactate, and unsaturated fatty acid. Change in taurine was only observed in the separation comparison of high-dose group and control. In urine, the variation metabolites included elevations in glucose, creatine, and TMAO as well as decreased lactate, succinate, α-ketoglutaric acid, citrate and hippurate in low-dose group compared with control. Only alanine and creatine were decreased significantly in high-dose group compared with control.
Nux Vomica induced disruptions in glycolysis, lipid and amino acid metabolism, and toxic effects were aggravated in liver and kidney tissues as dosing time was prolonged. 1H NMR-based metabonomics combined with biochemical and histopathological methods can be applied to elucidate the toxicity mechanism of Nux Vomica decoction that caused liver and kidney injuries in rats.
Involvement of Organic Cation Transporters in the Kinetics of Trimethylamine N-oxide
2017, Journal of Pharmaceutical SciencesRecent studies suggest that trimethylamine N-oxide (TMAO) is associated with the development of chronic kidney disease and heart failure. In this study, we investigated the importance of organic cation transporters (OCTs) in the clearance and tissue distribution of TMAO. The low-affinity and high-capacity transport of TMAO by mouse and human OCT1 and OCT2 was observed. Uptake and efflux of TMAO by the mouse hepatocytes as well as TMAO uptake into mouse kidney slices were significantly decreased by the addition of tetraethylammonium or Oct1/2 double knockout (dKO). Plasma concentrations of endogenous TMAO and TMAO-d9 given by intravenous infusion was 2-fold higher in Oct1/2 dKO than in wild-type mice due to significant decrease in its renal clearance. These results indicate that OCTs have a crucial role in the kinetics of TMAO in mice. In human, however, the OCT2-mediated tubular secretion in the urinary excretion of TMAO was insignificant because the renal clearance of TMAO was similar to that of creatinine in both young and elderly subjects, suggesting the species difference in the urinary excretion mechanisms of TMAO between mouse and human.
<sup>1</sup>H NMR and MVA metabolomic profiles of urines from piglets fed with boluses contaminated with a mixture of five mycotoxins
2017, Biochemistry and Biophysics ReportsMetabolic profile of urine from piglets administered with single boluses contaminated with mycotoxin mixture (deoxynivalenol, aflatoxin B1, fumonisin B1, zearalenone, and ochratoxin A) were studied by 1H NMR spectroscopy and chemometrics (PCA, PLS-DA, and OPLS-DA). The mycotoxin levels were close to the established maximum and guidance levels for animal feed (2003/100/EC and 2006/576/EC). Urine samples were obtained from four groups of four piglets before (control, C) or within 24 h (treated, T) after receiving a contaminated boluses with increasing doses of mycotoxins (boluses 1–4). For the two highest dose groups, the urines were collected also after one week of wash out (W). For the two lowest doses groups no significant differences between the C and T samples were observed. By contrast, for the two highest doses groups the T urines separated from the controls for a higher relative content of creatinine, p-cresol glucuronide and phenyl acetyl glycine and lower concentration of betaine and TMAO. Interestingly, a similar profile was found for both W and T urines suggesting, at least for the highest doses used, serious alteration after a single bolus of mycotoxin mixture.